## Person: Garay Elizondo, Luis Javier

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##### First Name

Luis Javier

##### Last Name

Garay Elizondo

##### Affiliation

Universidad Complutense de Madrid

##### Faculty / Institute

Ciencias Físicas

##### Department

Física Teórica

##### Area

Física Teórica

##### Identifiers

16 results

## Search Results

Now showing 1 - 10 of 16

Publication Where Does the Physics of Extreme Gravitational Collapse Reside?(MDPI, 2016-05-13) Barceló, Carlos; Carballo-Rubio, Raúl; Garay Elizondo, Luis JavierThe gravitational collapse of massive stars serves to manifest the most severe deviations of general relativity with respect to Newtonian gravity: the formation of horizons and spacetime singularities. Both features have proven to be catalysts of deep physical developments, especially when combined with the principles of quantum mechanics. Nonetheless, it is seldom remarked that it is hardly possible to combine all these developments into a unified theoretical model, while maintaining reasonable prospects for the independent experimental corroboration of its different parts. In this paper we review the current theoretical understanding of the physics of gravitational collapse in order to highlight this tension, stating the position that the standard view on evaporating black holes stands for. This serves as the motivation for the discussion of a recent proposal that offers the opposite perspective, represented by a set of geometries that regularize the classical singular behavior and present modifications of the near-horizon Schwarzschild geometry as the result of the propagation of non-perturbative ultraviolet effects originated in regions of high curvature. We present an extensive exploration of the necessary steps on the explicit construction of these geometries, and discuss how this proposal could change our present understanding of astrophysical black holes and even offer the possibility of detecting genuine ultraviolet effects in gravitational-wave experiments.Publication Black holes turn white fast, otherwise stay black: no half measures(Springer, 2016-01-26) Barceló, Carlos; Carballo Rubio, Raúl; Garay Elizondo, Luis JavierRecently, various authors have proposed that the dominant ultraviolet effect in the gravitational collapse of massive stars to black holes is the transition between a black-hole geometry and a white-hole geometry, though their proposals are radically different in terms of their physical interpretation and characteristic time scales [1, 2]. Several decades ago, it was shown by Eardley that white holes are highly unstable to the accretion of small amounts of matter, being rapidly turned into black holes [3]. Studying the crossing of null shells on geometries describing the black-hole to white-hole transition, we obtain the conditions for the instability to develop in terms of the parameters of these geometries. We conclude that transitions with long characteristic time scales are pathologically unstable: occasional perturbations away from the perfect vacuum around these compact objects, even if being imperceptibly small, suffocate the white-hole explosion. On the other hand, geometries with short characteristic time scales are shown to be robust against perturbations, so that the corresponding processes could take place in real astrophysical scenarios. This motivates a conjecture about the transition amplitudes of different decay channels for black holes in a suitable ultraviolet completion of general relativity.Publication Two formalisms, one renormalized stress-energy tensor(American Physical Society, 2012-04-02) Barceló, Carlos; Carballo-Rubio, Raúl; Garay Elizondo, Luis JavierWe explicitly compare the structure of the renormalized stress-energy tensor of a massless scalar field in a (1 + 1) curved spacetime as obtained by two different strategies: normal-mode construction of the field operator and one-loop effective action. We pay special attention to where and how the information related to the choice of vacuum state in both formalisms is encoded. By establishing a clear translation map between both procedures, we show that these two potentially different renormalized stress-energy tensors are actually equal, when using vacuum-state choices related by this map. One specific aim of the analysis is to facilitate the comparison of results regarding semiclassical effects in gravitational collapse as obtained within these different formalisms.Publication Interpretations and naturalness in the radiation-reaction problem(MDPI, 2021-04-12) Barceló, Carlos; Garay Elizondo, Luis Javier; Redondo Yuste, JaimeAfter more than a century of history, the radiation-reaction problem in classical electrodynamics still surprises and puzzles new generations of researchers. Here, we revise and explain some of the paradoxical issues that one faces when approaching the problem, mostly associated with regimes of uniform proper acceleration. The answers we provide can be found in the literature and are a synthesis of a large body of research. We only present them in a personal way that may help in their understanding. Besides, after the presentation of the standard answers, we motivate and present a twist to those ideas. The physics of emission of radiation by extended charges (charges with internal structure) might proceed in a surprising oscillating fashion. This hypothetical process could open up new research paths and a new take on the equivalence principle.Publication Emergent gauge symmetries: Yang-Mills theory(Springer, 2021-05-02) Barceló, Carlos; Carballo Rubio, Raúl; Garay Elizondo, Luis Javier; García Moreno, GerardoIn this article, subleading (in 1/N) corrections to the action of the one loop dilatation operator in the su(3) sector of N = 4 super Yang-Mills theory are studied. We focus on the system of operators dual to two giant graviton systems, which have a bare dimension ∼ O(N) and are a linear combination of restricted Schur polynomials with p = 2 long columns. At the leading order the dilatation operator gives rise to the free part of an emergent Yang-Mills theory, arising from the open string excitations of the giant gravitons. We verify that the terms we study describe interactions between these open string excitations. The interactions have the U(1)×U(1) gauge invariance expected for a pair of separated branes.Publication Vacuum Semiclassical Gravity Does Not Leave Space for Safe Singularities(MDPI, 2021-08-01) Arrechea, Julio; Barceló, Carlos; Boyanov Savov, Valentin; Garay Elizondo, Luis JavierGeneral relativity predicts its own demise at singularities but also appears to conveniently shield itself from the catastrophic consequences of such singularities, making them safe. For instance, if strong cosmic censorship were ultimately satisfied, spacetime singularities, although present, would not pose any practical problems to predictability. Here, we argue that under semiclassical effects, the situation should be rather different: the potential singularities which could appear in the theory will generically affect predictability, and so one will be forced to analyse whether there is a way to regularise them. For these possible regularisations, the presence and behaviour of matter during gravitational collapse and stabilisation into new structures will play a key role. First, we show that the static semiclassical counterparts to the Schwarzschild and Reissner–Nordström geometries have singularities which are no longer hidden behind horizons. Then, we argue that in dynamical scenarios of formation and evaporation of black holes, we are left with only three possible outcomes which could avoid singularities and eventual predictability issues. We briefly analyse the viability of each one of them within semiclassical gravity and discuss the expected characteristic timescales of their evolution.Publication Analogue gravity simulation of superpositions of spacetimes(Springer, 2022-08-20) Barceló, Carlos; Garay Elizondo, Luis Javier; García Moreno, GerardoTaking the principles of quantum mechanics as they stand and applying them to gravity, leads to the conclusion that one might be able to generate superpositions of spacetimes, at least formally. We analyze such a possibility from an analogue gravity perspective. We present an analogue toy model consisting of a Bose-Einstein condensate in a double-well potential and identify the states that could potentially be interpreted as superposition of effective spacetimes. These states are unstable and the source of instability from a microscopic point of view can be related to the absence of a well-defined causal structure in the effective geometric description. We explore the consequences of these instabilities and argue that they resonate with Penrose's ideas about the decay that superpositions of states with sufficiently different gravitational fields associated should experience.Publication Quantum non-gravity and stellar collapse(Springer, 2011-09) Barceló, Carlos; Garay Elizondo, Luis Javier; Jannes, GilObservational indications combined with analyses of analogue and emergent gravity in condensed matter systems support the possibility that there might be two distinct energy scales related to quantum gravity: the scale that sets the onset of quantum gravitational effects E-B ( related to the Planck scale) and the much higher scale E-L signalling the breaking of Lorentz symmetry. We suggest a natural interpretation for these two scales: E-L is the energy scale below which a special relativistic spacetime emerges, E-B is the scale below which this spacetime geometry becomes curved. This implies that the first 'quantum' gravitational effect around E-B could simply be that gravity is progressively switched off, leaving an effective Minkowski quantum field theory up to much higher energies of the order of E-L. This scenario may have important consequences for gravitational collapse, inasmuch as it opens up new possibilities for the final state of stellar collapse other than an evaporating black hole.Publication Warp drive aerodynamics(Springer, 2022-08-29) Barceló, Carlos; Boyanov Savov, Valentin; Garay Elizondo, Luis Javier; Martín Martínez, Eduardo; Sánchez Velázquez, José ManuelIn this work we analyse the potential for a warp drive spacetime to develop instabilities due to the presence of quantum matter. Particularly, we look for points of infinite blueshift (which are analogous to points of a black hole inner horizon, known for its semiclassical instability), and categorise them through the behaviour of geodesics in their vicinity. We find that warp-drive bubbles in dimension 2+1 or higher are in fact likely to be stable, as they generally contain only isolated points where divergences are approached, leading to a finite limit for the overall accumulation of destabilising energy. Furthermore, any semiclassical instabilities in the warp drive due to energy-density buildups can be further diminished with particular, more "aerodynamic" shapes and trajectories for the drive.Publication Hawking radiation as perceived by different observers: an analytic expression for the effective-temperature function(IOP Publishing Ltd, 2012-04-12) Barbado, L. C.; Barceló, Carlos; Garay Elizondo, Luis JavierGiven a field vacuum state in a black hole spacetime, this state can be analysed in terms of how it is perceived (in terms of particle content) by different observers. This can be done by means of the effective-temperature function introduced by Barcelo et al (2011 Phys. Rev. D 83 041501). In Barbado et al (2011 Class. Quantum Grav. 28 125021), this function was analysed in a case-by-case basis for a number of interesting situations. In this work, we find a general analytic expression for the effective-temperature function which, apart from the vacuum state choice, depends on the position, the local velocity and the acceleration of the specific observer. We give a clear physical interpretation of the quantities appearing in the expression, and illustrate its potentiality with a few examples.